This invention is directed to the measurement of resistors and in particular to the measurement of resistors under ac conditions.
The measurement of resistors in the range from less than 1 .OMEGA. to over 1 M.OMEGA. at direct currents with better than one ppm accuracy has been carried out using a dc comparator bridge as described in the publication entitled, "A Direct Current Comparator Bridge for High Resistance Measurements", by N. L. Kusters and M. P. MacMartin, IEEE Trans. on Instrumentation and Measurements, Vol. IM-22, No. 4, pp 382-386, December 1973.
However, power resistors which have the same dc resistance do not always have the same reactive component and therefore do not act in the same manner under ac conditions. It is preferred for many applications to be able to measure both the resistive and the reactive components of resistances under ac conditions. Until the present invention, an ac comparator bridge had not been developed though a "Current Comparator for Power and Energy Measurements" is described in U.S. Pat. No. 3,849,727 which issued on Nov. 19, 1974 to N. L. Kusters et al.